CN101393172A - Non-damage detection for cracks in solid by non-linear resonating sound spectrum method - Google Patents

Abstract

The invention relates to a nonlinear resonance sound spectrum method for carrying out nondestructive detection on crack in a solid. The method comprises the following steps: a probe prepared from a piezoelectric material is adopted to emit sound wave to a solid material standard bar with one fixed end and one free end; a sound signal passing through a solid material is received by an accelerometer; the frequency of the sound wave excitated by the probe is the resonant frequency of the solid material standard bar; a power spectrum of the received signal is analyzed by a FFT method, thereby obtaining the size of ultraharmonics; and according to the relation between the position of the crack on the solid material standard bar and the ultraharmonics, the position of the crack on the actual solid material is reversely deduced. The method can carry out nondestructive detection on microcrack of the solid; and an obtained parameter is more sensitive to the change of the crack than a linear acoustic parameter.

Description

Crackle in the nonlinear resonance sound spectrum method Non-Destructive Testing solid

One, technical field

The present invention relates to the new method of the crackle in the Non-Destructive Testing solid, promptly adopt nonlinear resonance sound spectrum method that the crackle of solid material is levied surely.

Two, background technology

Building materials in use can produce the phenomenon of aging and crackle, and crackle is present in the engineering structure in large quantities, how to discern their position and shape apace, is the main task of Non-Destructive Testing.In recent years, the application of Non-Destructive Testing (NDT) technology in industry develops to the direction of quantification and Nondestructive Evaluation (NDE).

The conventional method that is used for the crizzle detection at present has: [1～5] such as ultrasonic method, eddy-current method, gamma ray material testings.The ultimate principle of ultrasonic method: the character of utilizing ultrasound wave to propagate in medium judges that the defective of workpiece material is with unusual.Ultrasonic Detection mainly is transmission, reflection and the refraction effect that produces when utilizing ultrasound wave to run into heterogeneous interface in communication process, ultrasonic signal is analyzed and handled and extracts the feature of defective.

Along with science and technology development, many physical phenomenons constantly are used, and conventional method is constantly developed, and for example electromagnetic acoustic detection technique (EMATS) and laser-ultrasound detection technique also produce thereupon and be employed.The electromagnetic acoustic method is based on the reciprocation in eddy current and magnetic field, utilizes electromagnetic ultrasonic probe to produce and receive a kind of non-contact detection technology of supersonic guide-wave.It is a detection new technology that grew up in recent years that laser-ultrasound detects, it is radiated at the measured piece surface by the pulse laser beam that intensity is modulated and produces ultrasound wave, through changing experiment parameter, the laser-ultrasound source can inspire various guided waves such as compressional wave, shear wave, surface wave.Because ultrasonic signal both can be produced by laser pumping, can utilize optical means to detect again, therefore can realize complete non-contact detecting and fast scan imaging, be more convenient under mal-conditions such as high temperature, macroseism, realizing Non-Destructive Testing [6].In addition, utilize mode-locked laser, be easy to obtain the ultrasonic pulse close with laser pulse width, it is ultrasonic that its frequency band far is wider than conventional transducer and is produced, therefore, based on the defect detecting technique that the ultrasonic diffraction method forms, all very sensitive to the fine crack on measured piece surface and nearly surface, accuracy in detection is also than other lossless detection method height [7,8].

But the parameter that at present supersonic detection method of this material also just is limited to a kind of linearity, the defective of solid interior is surveyed in for example velocity of sound and acoustic attenuation by the variation of the velocity of sound and acoustic attenuation under the defectiveness situation.This method has obvious defects, and is promptly very sensitive to bigger defective, but very little to some, and very minute defects (such as crackle) is just very insensitive.So need a kind of new technology of development, can detect the position of the crackle of solid interior.

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[2]. Ying Chongfu. ultrasonics. Beijing: Science Press, 1990.

[3].C?B?Scruby.Some?application?of?laser?ultrasound.Ultrasonics，1989，127：195—209.

[4].Huge?savings?in?large?area?and?complex?surface?inspection?using?laserultrasonic.Insight，1996，38(1).

[5].Q?Shan.Surface?breaking?fatigue?crack?detection?using?laserultrasound.Appl?Phys，1993，62(21).

[6]. Shujuan WANG, Zhao Zaixin, Zhai Guofu is based on the train wheel crack detection system of electromagnetic acoustic, instrumental technique and sensor, 2005,11:27-29

[7]. Su Kun, appoint the sea, Lee builds, and You Zheng is based on the research of the micro-crack detection technique of laser-ultrasound, optical technology, 2002,28,6:518-522

[8].J?P?Monchalin.Laser?ultrasonic?developments?towards?industrialapplications.IEEE?Ultrasonics?Symposium.1988.

Three, summary of the invention

Studies show that under the resonance mode of solid bar, sound wave can produce non-linear phenomena clearly when propagating in having the solid of crackle, promptly except first-harmonic is arranged, also can produce higher hamonic wave, and odd harmonic is more more obvious than even-order harmonic, and this is a feature of non-classical nonlinear acoustics.The present invention seeks to: propose a kind of method of crackle of novel Non-Destructive Testing solid material, promptly nonlinear resonance sound spectrum method is promptly analyzed the variation of the higher hamonic wave in the received signal, detects the position of crackle.On this basis, can further study the damage of adopting the method to measure building materials, the degree of fatigue damage, utilize the method that nuclear power station, chemical plant facility, dam etc. are monitored by crack position, size that seismic activity causes, assist the design shockproof structure.

Technical scheme of the present invention: nonlinear resonance sound spectrum method detects the method for solid crackle and for the probe that adopts the piezoelectric preparation earlier solid material is launched sound wave, adopt accelerometer to receive by the acoustical signal behind the solid material, the frequency of the sound wave that probe excites is the resonant frequency of solid material (master bar), analyze the power spectrum of received signal with the FFT method, thereby obtain the size of higher hamonic wave; The position and the higher hamonic wave that go up crackle according to solid material (master bar) concern the anti-position that pushes away actual solid material crackle.

Utilization receives the anti-position that pushes away crackle of high-frequency harmonic component of signal, and according to theoretical analysis: when the ratio of known odd harmonic, we just can utilize the anti-position that pushes away crackle of following formula:

Adopt an end to fix, the mode of the free asymmetric boundary condition of an end, can know by inference:

When $\frac{X_{\mathrm{5,1}}}{X_{\mathrm{3,1}}}=s---\left(1\right)$

The free-ended position X of crackle distance _d:

$\frac{x_d}{L}=\frac{1}{\mathrm{\π}}\mathrm{arc}\sin \sqrt{\frac{(100-84s)\±\sqrt{{(100-84s)}^2-4\×80\×(25-63s)}}{160}}---\left(2\right)$

Here: L is that rod is long, X _3,1And X _5,1Be the third harmonic under first resonance mode and the amplitude of quintuple harmonics.Can obtain similar result in second pattern.

The advantage that the present invention compared with prior art has is: existing acoustic method is to adopt linear method, promptly adopt the velocity of sound and acoustic attenuation, can only detect the bigger defective of yardstick, and the method that the present invention proposes can detect micron-sized crackle, can provide reference frame to the early fatigue of solid material.

The characteristics of structure of the present invention are: excite transducer under the resonance mode of solid bar, come received signal with accelerometer, analyze its frequency spectrum then, thereby obtain its each time high-order harmonic wave size.According to the relation of high-order harmonic wave and crack position, in conjunction with the skew of nonlinear resonance frequency, the anti-position that pushes away crackle.

Four, description of drawings

Fig. 1 experimental system block diagram

The experimental result of Fig. 2 reference sample

The experimental result of the damaged sample of Fig. 3

Fig. 3 (a) is damaged apart from free end 120mm; Fig. 3 (b) is damaged apart from free end 40mm.

Five, embodiment

Experimental system measurement block diagram is seen shown in Figure 1, is the correctness of proof theory, and we have made the series of concrete sample transmitted acoustic pulse is analyzed.Concrete sample, is inserted the model after coagulation that plank makes and is formed in 1:3 ratio mixing and stirring by cement and fine sand.The plank model is a rectangular parallelepiped, and unification is of a size of long 0.16m, wide 0.06m, high 0.06m.For observing non-classical non-linear, we have artificially made the existence of a damaged regional simulating crack on a sample.Concrete method for making is 0.012m place on the sample length direction, and the hollow plastic conduit of imbedding two ends sealing replaces crackle, and plastics pipe range 0.03m, diameter are 0.003m.

During experiment, receiving transducer and transmitting transducer place the two ends of concrete long respectively, sample first resonant frequency is about 4kHz, second resonant frequency is about 10KHz, because transducer bandwidth and Power Limitation, we are chosen under second resonance mode and experimentize, and signal adopts modulation signal, pulsewidth is 10ms, contains 50 cycles in the pulsewidth.For harmless sample, transmit and get 300mv, the power spectrum of transmission signal such as Fig. 2.Can know that from figure (2) second resonant frequency of harmless sample is 10.006KHz, classical non-linear minimum for the influence of the higher hamonic wave more than three times, can ignore, but still very obvious to the second harmonic influence.Sample replaced with diminish sample, this moment is damaged be 120mm apart from free end (accelerometer end), and when transmitting to 300mv, the power spectrum signal that receives is Fig. 3 a, and the skew of nonlinear resonance frequency is 94Hz at this moment.With 180 ° of sample counter-rotatings, this moment is damaged to be 40mm apart from free end (accelerometer end), and the power spectrum signal that receives is Fig. 3 b, and this moment, the skew of nonlinear resonance frequency was 18Hz.

According to formula (2), in conjunction with the skew (defective is far away more from free end, and nonlinear resonance frequency deviation is big more) of nonlinear resonance frequency.The defective locations that we obtain first kind of situation sample is $x_d=123.1\mathrm{mm}(s=\frac{X_{\mathrm{5,1}}}{X_{\mathrm{3,1}}}=0.121);$ The defective locations of second kind of situation sample is $x_d=43.8\mathrm{mm}(s=\frac{X_{\mathrm{5,1}}}{X_{\mathrm{3,1}}}=0.207);$ Identical substantially with the actual defects position.

Claims (3)

1, the method for the crackle in the nonlinear resonance sound spectrum method Non-Destructive Testing solid: the probe that it is characterized in that adopting earlier the piezoelectric preparation to an end fix, end solid material master bar emission freely sound wave, adopt accelerometer to receive by the acoustical signal behind the solid material, the frequency of the sound wave that probe excites is the resonant frequency of solid material master bar, analyze the power spectrum of received signal with the FFT method, thereby obtain the size of higher hamonic wave; According to the position and the higher hamonic wave relation of crackle on the solid material master bar, the anti-position that pushes away actual solid material crackle:

Adopt an end to fix, the mode of the free asymmetric boundary condition of an end, know by inference:

When $\frac{X_{\mathrm{5,1}}}{X_{\mathrm{3,1}}}=s---\left(1\right)$

The free-ended position X of crackle distance _d:

$\frac{x_d}{L}=\frac{1}{\mathrm{\π}}\arcsin \sqrt{\frac{(100-84s)\±\sqrt{{(100-84s)}^2-4\×80\×(25-63s)}}{160}}---\left(2\right)$

Here: L is that rod is long, X _3,1And X _5,1Be the third harmonic under first resonance mode and the amplitude of quintuple harmonics.Can obtain similar result in second pattern.

2, the method for nonlinear resonance sound spectrum method Non-Destructive Testing solid crackle according to claim 1: the sample that it is characterized in that transmitting terminal support and load by experiment is closely linked, thereby guarantees that transmitting terminal is absolute bounds, i.e. stiff end; Accelerometer links by the other end of couplant and sample, and the aluminium sheet that adds a 0.09kg between sample and acceleration is to increase the coupling between them.The general assembly (TW) of accelerometer and aluminium sheet is very light, therefore can regard sound-soft boundary, i.e. free end as.

3, the method for nonlinear resonance sound spectrum method Non-Destructive Testing solid crackle according to claim 1: it is characterized in that adopting two kinds of samples to be used for experiment, a kind of is the sample that cement and fine sand mix, and does not have the landfill of plastic tube, and we are referred to as reference sample.Another kind is damaged sample, at cement and fine sand potpourri the landfill of a hollow plastic pipe is arranged, and the orientation of plastic tube is vertical with the length direction of sample, and the mid point of the position of filling material and rod is at a distance of 40mm.First kind of situation in the experiment, plastic tube in the damaged sample and free-ended distance are 120mm; Second kind of situation in the experiment, with 180 ° of sample counter-rotatings, plastic tube in the damaged sample and free-ended distance are 40mm.

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